Since 1978, a longitudinal study investigating the effects of marihuana and cigarettes used during pregnancy has been underway. The overall purpose of this Ottawa Prenatal Prospective Study is to examine the effects of these drugs on pregnancy, the neonate and the young child. The general objective of this competitive renewal is to determine whether particular developmental delays and behavioral difficulties observed in the newborn, infant, and young child that are' statistically associated, in a differential fashion, with prenatal marihuana and cigarette exposure persist in the 6 & 7 year old child and whether, by an in depth neurobehavioural assessment, a greater degree of specificity of dysfunction can be identified., Additionally, because of the longitudinal nature of the work, the predictive validity of the infant tests can be examined as can the continuity of effects over age. The neurobehavioural battery will include an assessment of fine and gross motor abilities, sensory skills (tactile, visual & auditory), kinesthetic functioning, visual-spatial capabilities, language skills, reasoning ability, memory (visual, tactile and language), intelligence, academic readiness, phonemic awareness and overall behavior. Maternal variables (e.g. health, nutrition, parity, age, other drugs, intelligence) and postnatal, environmental variables ( e.g. home environment, second-hand smoke, preschool experience) will be included in multivariate statistical analyses. The Ottawa study is the only work to have published data on marihuana offspring beyond a year of age and is the most comprehensive longitudinal work examining 6-7 year old children of cigarettes smokers. The testing of children of this age is particularly critical as the identification of subtle learning difficulties is most likely to come from studies of this age group.